Intravenous drug additive systems have been used in patient care for many years. These systems typically operate by gravity induced flow from a container into the patient.
Quite often it is desirable to add more than one fluid intravenously to the patient. While two or more separate venous entries may be made, each entry increases the risk of infection and other harmful results. Therefore, it has been recognized as desirable to employ a drug additive system in which a primary fluid is added intravenously with a secondary fluid being added intermittently through the same entry ("piggy backing") The primary fluid may function as fluid replacement, keep vein open (KVO) fluid, nutritional fluids, blood or other drugs. The secondary fluid may commonly be antibiotics, anticoagulants, antihypertensives, cardiovascular agents or other medicaments.
Traditionally, both primary and secondary fluids have been stored in glass bottles or flexible plastic bags suspended above the patient. A drip chamber is either to or integral with the bottle or bag. An orifice of predetermined diameter interconnects the drip chamber with the fluid in the container. A flexible tube extends from the container to the patient. An early form of single fluid delivery system employing gravity, still widely used, incorporates the drip chamber and a manually set pinching device. A nurse or aide may visually count the drop rate in the chamber and manually set the pinching device on the delivery tubing to achieve a desired flow rate. Fluid delivery systems of this type are not highly accurate. The volume of each drop of fluid dripping into the drip chamber may not be uniform. The drop size is dependent on the orifice diameter, which may vary within a manufacturing tolerance for a particular intravenous giving set manufactured. In addition, even the nominal orifice diameter is not uniform throughout the industry. Manufactures sell drip chambers having 10, 15, 20 and 60 drops/milliliter, for example. Confusion and improper application can result. The volume of the fluid drops may also vary with temperature and viscosity.
The gravitational head pressure which acts to infuse the fluid into the patient may vary. In addition, the tubing cooperating with the pinching device may relax, varying the restriction of flow and permitting inaccuracy in delivery to the patient.
All of these problems require the nurse or aid to be continuously vigilant of the flow rate and permit error.
Drop counting has been used for many years as the standard technique for flow control in IV applications because of its relative simplicity. However, the goal in infusion is to accurately determine the volume of fluid infused.
Although such systems suffer from the inaccuracies noted above and require special attention from nursing personnel, they have formed the basis for additive or "piggyback" systems to introduce a secondary fluid. Such arrangements are described for example in a brochure entitled "New Concepts in Intermittent IV Therapy", published by Travenol Laboratories Inc., Deerfield, Ill. In a typical prior art set up, the secondary fluid or medicament container is elevated above the level of the primary fluid container. A check valve is placed in the line extending from the primary container and the lines from both containers are connected through a Y-connector to a single delivery line for delivery to a patient. The gravitational head of the secondary fluid in the secondary container closes the check valve to prevent flow from the primary container. The system will deliver the secondary fluid to the patient and thereupon automatically commence delivery of the primary fluid as the check valve opens. The delivery of both fluids, however, is made with the same inaccuracies noted above inherent in this type of system. Moreover, the large number of manipulations necessary by the nurse or aide in the operation of this system gives rise to the potential for error. Unless adjustment is made by the nurse after the secondary fluid delivery is complete, both fluid deliveries operate through the same pinch setting.
One technique for improving on the accuracy of intravenous delivery has been the use of positive pressure volumetric pumps which force fluid into the patient. One such pump is sold as the LifeCare IV pump system manufactured by Abbott Laboratories, Hospital Products Division, North Chicago, Ill. 60064. While positive pressure volumetric pumps improve the accuracy of delivery of the fluid compared to the prior described system, several disadvantages exist.
The positive pressure generated by the pump increases the dangers from potential infiltration of the fluid into the tissues of the patient which can result from improper catheter placement. When employed with a "piggyback" delivery system with the pump downstream of the Y-connector, the pump will draw both primary and secondary fluids from both containers until the secondary container, which commonly has a smaller capacity than the primary container, is empty. Therefore, the secondary fluid is diluted with the primary fluid at an unknown rate. In addition, the known pumps typically provide only a single flow rate once the pump is set.
One improvement in the use of positive volumetric pressure pumps has been to manually clamp the primary fluid delivery line to insure the infusion of the secondary fluid at full strength. However, this requires the nurse to return to bedside to manipulate the clamp after the secondary infusion is complete, and monitor the flow to begin the primary fluid infusion. In addition, the potentially serious problems from infiltration remain. A pump may be positioned in the secondary delivery line of the system to deliver the secondary fluid under positive pressure. However, the nurse must also return to the bedside after the secondary fluid is exhausted and the danger of infiltration remains a concern.
Drop counting controllers which include drop sensors for monitoring the drip rate in a drip chamber and controlling a tube pinch device have been employed with a piggyback system. One such controller is manufactured by Imed Corporation of 9925 Carroll Canyon Road, San Diego, Calif. as model 350.
The drop counting controllers have several disadvantages. The drop sensors must rely on the accuracy of drop volume. The drop counting controller operates by sensing the passage of a drop past an optical or other sensor and computing the flow rate based on an assumed drop volume. The drip volume in actuality may differ, based on differing orifice diameters, viscosity or other causes noted above.
The typical drop counting controller includes only a single drop sensor. Therefore, the nurse or aide must position the drop sensor on the drip chamber of the secondary container to control the rate of infusion of the secondary fluid. The nurse or aide must monitor the flow of the secondary fluid to determine when the secondary fluid has been infused and subsequently move the drop sensor to the drip chamber of the primary container to control the rate of infusion of the primary fluid.
It has been suggested to improve the system by employing two drop counting controllers, each having drop sensors. One drop counting controller will have its drop sensor positioned at the drip chamber of the secondary container and will infuse the secondary fluid until the secondary container is empty. This controller then signals the other controller having its drop sensor at the drip chamber of the primary container to initiate infusion of the primary fluid. However, this system is also subject to the inaccuracies of the drip chamber. It is also expensive in duplicating elements of sensors and electronic sets.